A conventionally known gas treatment method separates an acid compound by bringing a gas to be treated which contains an acid compound into contact with a treatment liquid. As a gas treatment method of this kind, for example, as disclosed in Literature 1 (Takashi Tomikawa, other two persons, “Search and Study of Carbon Dioxide Absorbent Separating into Two Liquid Phases”, Society for Chemical Engineers, Japan, Annual Meeting, Fukuoka, 2014) and Literature 2 (Raynal, L., et al., The DMXTM process: an original solution for lowering the cost of post-combustion carbon capture, Energy Procedia, 4, 779-786, 2011), a method using a treatment liquid (absorbent) which liquid-phase-separates into a first phase portion having a high acid compound content and a second phase portion having a low acid compound content is well known.
The gas treatment device which executes the method disclosed in Literature 1 includes an absorber 71, a liquid separator 72, a heat exchanger 73, and a regenerator 74 as shown in FIG. 10. In the absorber 71, exhaust gas (gas to be treated) containing carbon dioxide, and an absorbent consisting of MEA (monoethanolamine), additive, and water come into contact with each other. The absorbent liquid-phase-separates into a first phase portion (CO2 rich phase) having a high carbon dioxide content and a second phase portion (CO2 lean phase) having a low CO2 content. In this state, the absorbent is sent to the liquid separator 72. The absorbent stored in the liquid separator 72 has a lower region in which the first phase portion is present and an upper region in which the second phase portion is present. The lower region absorbent is sent to the regenerator 74 because of a high carbon dioxide content. At this time, the absorbent is preheated in the heat exchanger 73. On the other hand, the upper region absorbent is returned to the absorber 71 because of a low carbon dioxide content. The absorbent separates carbon dioxide therefrom by heating in the regenerator 74. The carbon dioxide separated from the absorbent is collected through a collection path, while the absorbent having released carbon dioxide is returned to the absorber 71 via the heat exchanger 73. Literature 1 shows that a unit of energy when 2-(Methylamino)ethanol (MAE) is used as an amine compound is 2.7 GJ/t-CO2.
The gas treatment device disclosed in Literature 2, as shown in FIG. 11, has the same configuration as that of the device shown in FIG. 10, except that a liquid separator 72 is positioned between a heat exchanger 73 and a regenerator 74.
As a device which implements the above gas treatment method, such a configuration as disclosed in Literature 3 (Japanese Unexamined Patent Publication No. 2011-213494) is known which is provided with a heat pump but does not use a treatment liquid (absorbent) which liquid-phase-separates into a first phase portion and a second phase portion. Use of a heat pump enables use of heat generated by heating reaction in an absorber as a heat source of heat absorbing reaction in a regenerator. Accordingly, a heat input from the outside can be suppressed.
In the gas treatment methods disclosed in Literatures 1 and 2, while an absorbent containing the first phase portion having a high carbon dioxide content is sent to a regenerator, an absorbent containing the second phase portion having a low carbon dioxide is returned to the absorber. This is based on a technical idea that removing the second phase portion having a low carbon dioxide to reduce a ratio of water in a treatment liquid introduced into the regenerator enables reduction in energy necessary for heating a treatment liquid in the regenerator. On the other hand, it is demanded to further reduce energy necessary for separately collecting an acid compound.